2,6-xylenol is produced by catalytically reacting phenol and methanol in a fixed-bed reactor under reaction conditions of normal pressure, gaseous phases and high temperature ranging from 300.degree. C. to 650.degree. C. The 2,6-xylenol is polymerized as poly-phenylene oxide which is a valuable engineering plastic material suitable for engineering and commercial applications by its good properties, such as: corrosion resistance and resistance to cold or hot water.
A conventional catalyst was disclosed by Arakawa Forest Chemical Industries, Ltd. in Japan Invention Publication No. 49-5928 (copy enclosed herewith as reference) for catalytic synthesis of 2,6-xylenol by mixing manganic oxide with ferric oxide, or by mixing manganic oxide with zinc oxide. However, such a conventional catalyst has the following defects:
1. The reaction of phenol and methanol to produce 2,6-xylenol is subjected to gaseous phases and exothermic reaction. If increasing the reaction temperature and pressure, the selectivity of product will be reduced and by-products will be increased to reduce the productivity. The major by-product is 2,4,6-trimethyl phenol which is very difficult to separate from the desired 2,6-xylenol.
Due to this reason, Arakawa process for synthesizing 2,6-xylenol was performed under normal pressure (1 Kg/cm.sup.2). In Arakawa process, if the Mn-Fe catalyst and the following reaction conditions are used:
Atomic ratio: Mn:Fe=99:1, PA1 Reaction temperature: 400.degree. C., PA1 Charging rate: 15 ml/hr, PA1 Liquid weight hourly space velocity (WHSV); b 0.439 l/hr, the productivity of 2,6-xylenol is very low and is only 0.1669 g/g-cat.hr.
2. During the synthesis of 2,6-xylenol by reacting phenol and methanol, methanol is consumed and decomposed into carbon monoxide and hydrogen. The consumption of methanol will reduce the concentration of methanol for the reaction and thus reduce the conversion rate of phenol and reduce the selectivity to 2,6-xylenol. If the yield of 2,6-xylenol is 94.70%, the methanol utilization efficiency is only 36.35%. Such a low methanol utilization efficiency is too low to have economic commercial value.
3. When making the catalyst by Arakawa process, the nitrate salts are decomposed into oxides which will release poisonous nitrogen dioxide to cause hazardous air pollution. The nitrogen dioxide will also react with water to form nitric acid which will corrode the contacted equipments.
4. The catalyst oxides of Arakawa process are formed through hot-melting decomposition so that the formed oxides have great density and are difficult for final processing.
The present inventors have found the defects of Arakawa process as abovementioned and invented the present process for making catalyst system for the synthesis of 2,6-xylenol.